I have a similar problem in my steering column/dash but the short rattle only occurs when going over small bumps/rougher roads at low speeds. BMW technician thought it was coming from the instrument cluster. They removed the instrument cluster and added felt tape and put it back in. ... Didn't work.
Not sure if I should bother taking the car back in. The noise does drive me crazy though. http://www.e90post.com/forums/images/smilies/iono.gif